Bluetooth amp kit sounds awful - anything I can do?
Discussion
I had the idea to take a broken 1960's classic transistor radio and convert it into a bluetooth speaker using a kit, but the sound is very harsh and distorted. Is there anything I can do to make it sound better. E.g wadding, porting, a passive radiator?
The speakers are mounted on 4mm ply.
This is the kit, I know 2 x 3W isn't going to shake the walls - https://www.kitronik.co.uk/c2160-bluetooth-stereo-...
The speakers are mounted on 4mm ply.
This is the kit, I know 2 x 3W isn't going to shake the walls - https://www.kitronik.co.uk/c2160-bluetooth-stereo-...
Edited by gmaz on Thursday 19th April 21:56
Tony1963 said:
I've just zoomed in and noticed that the speakers are only 4 ohm impedance. Usually a 4 ohm speaker would require a lot of power to do anything audible. I might be wrong, perhaps others here can go further?
I think those speakers are supplied with the kit, so I'd be surprised if they didn't work (they're rated at 5W: https://shop.pimoroni.com/products/5w-4-ohm-65mm-f...Does it sound the same if the speakers are removed from the cabinet? I wonder if the cones aren't moving freely.
Edited by Monty Python on Wednesday 11th April 18:51
nyt said:
Is your power supply up to the job?
Have you tried using one of the high capacity phone top up batteries that seem to be everywhere these days to test it?
It's the battery that came with the kit, so I hope so.Have you tried using one of the high capacity phone top up batteries that seem to be everywhere these days to test it?
I've now bought a different board off ebay and a 2 x 3.7v Li-Ion battery pack so once I've swapped the components I'll try again.
https://www.ebay.co.uk/itm/DC5V-2-6W-2-channel-Ste...
Have you kept the left and right speaker wires completely separate, and not joined the common (-) together?
Those boards operate in bridged mode - which means that the speaker outputs need to be completely floating.
Also - have you wired the (+) of the board to the (+) of each speaker - because if you have got the speakers out of phase, the sound will be tinny (but not necessarily distorted).
Finally - postimg.org seems to be dead - you might want to post your images somewhere else.
Those boards operate in bridged mode - which means that the speaker outputs need to be completely floating.
Also - have you wired the (+) of the board to the (+) of each speaker - because if you have got the speakers out of phase, the sound will be tinny (but not necessarily distorted).
Finally - postimg.org seems to be dead - you might want to post your images somewhere else.
TonyRPH said:
Have you kept the left and right speaker wires completely separate, and not joined the common (-) together?
Those boards operate in bridged mode - which means that the speaker outputs need to be completely floating.
Also - have you wired the (+) of the board to the (+) of each speaker - because if you have got the speakers out of phase, the sound will be tinny (but not necessarily distorted).
Finally - postimg.org seems to be dead - you might want to post your images somewhere else.
Yep I think I've done all that correctly, its a pretty simple kit.Those boards operate in bridged mode - which means that the speaker outputs need to be completely floating.
Also - have you wired the (+) of the board to the (+) of each speaker - because if you have got the speakers out of phase, the sound will be tinny (but not necessarily distorted).
Finally - postimg.org seems to be dead - you might want to post your images somewhere else.
Images have been restored, thanks for the warning.
Now I can see your images, the wiring looks fine and you've done a very neat job there.
No idea why it doesn't sound any good unfortunately.
Are you able to bypass the blue tooth and plug an audio source directly into it to test?
Sometimes blue tooth doesn't offer the best quality imho.
No idea why it doesn't sound any good unfortunately.
Are you able to bypass the blue tooth and plug an audio source directly into it to test?
Sometimes blue tooth doesn't offer the best quality imho.
Indeed, that is a tidy job. Well done.
Bad sound? Could be a number of reasons, but you aren't playing with the best of kit. BT (depending upon the type) can be a bit ropey, you don't have a great amp and the speakers are not the finest either. You aren't going to make a silk purse from a sow's ear and £6.50's worth of kit (incl shipping from China) means you aren't competing with Linn and Sonos. However that doesn't mean that you can't get the most from the kit you have.
As Tony said, can you try with a different audio source? Try and find the weakest point of the system and improve on that.
Are the speakers well sealed around the front? You could try baffling them; build a small box around the back of each one (keeping them separate). Without knowing the TS parameters you will be guessing but aim for about 120ml and see how you get on. Seal them well and see what that does for the sound.
Check all the connections. You have done a very tidy job (well done) but check and double-check everything to make sure it is correct.
How are you powering this thing? I can see the battery inside the radio. Does it sound better when plugged into the power supply as well? This could imply a lack of power to make things work to their best.
I fear your fundamental problem is that you have a poor source, a less-than-optimal amp and not great speakers and hence your results will be limited but you can probably squeeze an improvement out of it yet. Keep working on it and bear in mind (seriously) that you've made a pretty thing, and the ultimate sound quality isn't the be-all and end-all of the end product.
Bad sound? Could be a number of reasons, but you aren't playing with the best of kit. BT (depending upon the type) can be a bit ropey, you don't have a great amp and the speakers are not the finest either. You aren't going to make a silk purse from a sow's ear and £6.50's worth of kit (incl shipping from China) means you aren't competing with Linn and Sonos. However that doesn't mean that you can't get the most from the kit you have.
As Tony said, can you try with a different audio source? Try and find the weakest point of the system and improve on that.
Are the speakers well sealed around the front? You could try baffling them; build a small box around the back of each one (keeping them separate). Without knowing the TS parameters you will be guessing but aim for about 120ml and see how you get on. Seal them well and see what that does for the sound.
Check all the connections. You have done a very tidy job (well done) but check and double-check everything to make sure it is correct.
How are you powering this thing? I can see the battery inside the radio. Does it sound better when plugged into the power supply as well? This could imply a lack of power to make things work to their best.
I fear your fundamental problem is that you have a poor source, a less-than-optimal amp and not great speakers and hence your results will be limited but you can probably squeeze an improvement out of it yet. Keep working on it and bear in mind (seriously) that you've made a pretty thing, and the ultimate sound quality isn't the be-all and end-all of the end product.
I was just having a look at the datasheet for the IC they're using (PAM8008) and it looks as though they've mixed up the left / right speaker connections on the PCB.
Firstly I realise this will have minimal effect on the sound.
Here is the IC from the datasheet, which shows pins 14 and 16 as the right output and pins 9 and 11 as the left output.
Image is rotated to match the board layout.
And here is their board (it's not clear in the image, however I'm assuming that the notch indicating pin 1 is at the bottom edge of the IC in this image)
Their board indicates that pins 14 and 16 are left output and pins 9 and 11 are right output...
If I'm correct, then one does wonder if there are any other errors present on the board?
ETA: OP, I also note from the datasheet that the minimum supply voltage is 2.5V and max. is 5.5V.
Have you tried powering it from a USB adaptor to see if that helps? Your battery voltage might be borderline.
"2.4W Output at 1% THD with a 4 Load and 5V Power Supply "
Which means with a battery that's hovering around 3V I suspect you'll get about 0.75W (see graph below) - left axis is in mW - 1000mW = 1W
Firstly I realise this will have minimal effect on the sound.
Here is the IC from the datasheet, which shows pins 14 and 16 as the right output and pins 9 and 11 as the left output.
Image is rotated to match the board layout.
And here is their board (it's not clear in the image, however I'm assuming that the notch indicating pin 1 is at the bottom edge of the IC in this image)
Their board indicates that pins 14 and 16 are left output and pins 9 and 11 are right output...
If I'm correct, then one does wonder if there are any other errors present on the board?
ETA: OP, I also note from the datasheet that the minimum supply voltage is 2.5V and max. is 5.5V.
Have you tried powering it from a USB adaptor to see if that helps? Your battery voltage might be borderline.
"2.4W Output at 1% THD with a 4 Load and 5V Power Supply "
Which means with a battery that's hovering around 3V I suspect you'll get about 0.75W (see graph below) - left axis is in mW - 1000mW = 1W
Edited by TonyRPH on Friday 20th April 10:38
I would guess as others have suggested that in broad WYHIWYG (H for hear rather than S for see 
).
There's datasheet and app. note for the bluetooth module BM20 on Microchip website if you haven't already got 'em.
It looks to me that there is an aux in to the BT module if you can get at the pins with loopback straight to the out so that might remove the RF layer from the signal path.
You could also try substituting the speakers with your hifi ones. Not much volume as they'll likely be 8R.
Lastly also if you can get at the pins you could take the BT module out/amp IC inputs to a line in on your hifi, that'd remove the little speakers & the amp form the signal path.
You'd need some mildy ninja soldering skills as the pins are pretty tiny and if you do attempt it use very fine wire and strain relieve them as near t the pin as possible e.g. dab of hot melt adhesive,
regards,
Jet
).There's datasheet and app. note for the bluetooth module BM20 on Microchip website if you haven't already got 'em.
It looks to me that there is an aux in to the BT module if you can get at the pins with loopback straight to the out so that might remove the RF layer from the signal path.
You could also try substituting the speakers with your hifi ones. Not much volume as they'll likely be 8R.
Lastly also if you can get at the pins you could take the BT module out/amp IC inputs to a line in on your hifi, that'd remove the little speakers & the amp form the signal path.
You'd need some mildy ninja soldering skills as the pins are pretty tiny and if you do attempt it use very fine wire and strain relieve them as near t the pin as possible e.g. dab of hot melt adhesive,
regards,
Jet
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